The problems of asbestos fiber contamination and the removal of asbestos materials are well documented. Various types of containment structures have been utilized to control the airborne particulate matter such as asbestos fibers or other types of contaminants.
The prior structures generally are of two types. One time constructed, substantially permanent, type structures which generally are cumbersome and cannot be reutilized or portable structures which generally are not adapted to be utilized with negative air systems.
The prior portable structures generally are constructed from aluminum or rigid polyvinyl materials, which are not well suited for negative air utilization. Further, the closure structures of these portable structures, typically are formed by utilizing one or more flexible curtains. These curtains do not provide a suitable closure structure to maintain negative air control.
One improved portable negative air control unit is provided by parent application U.S. Ser. No. 07/277,772. The unit includes two or more door structures, which are substantially rigid and configured to maintain the negative air control. The door structures can be connected to the walls of various types of negative air structures.
One prior art system for controlling the negative air pressure in such structures provides for a free hanging flap or curtain. The flap is pulled open by the negative air flow and closes if negative air pressure is lost. To ensure no outward air leakage, the flap is configured larger than the opening to seal the opening shut. No variable adjustment is provided by the flap.
It would be desirable to provide an adjustable opening or orifice in negative air control structures to provide a variable air flow control for the structures.